Shielded balanced microwave analog multiplier

ABSTRACT

A completely shielded and balanced diode bridge, having biased diodes to insure dynamic balance and square-law operation, is fed by sum and difference signals from a hybrid ring drive which produces an output signal proportional to the product of the instantaneous amplitudes of the original microwave input signals applied to the hybrid ring drive.

United States Patent [72] Inventor John H. Malloy Silver Spring, Md.

[21] Appl. No. 871,442

[22] Filed Oct. 14, 1969 [45] Patented June 1, 1971 [73] Assignee The United State of America as represented by the Secretary of the Navy Continuation-impart of application Ser. No. 671,495, Sept. 28, 1967, now abandoned. This application Oct. 14, 1969, Ser. No. 871,442

[54] SHIELDED BALANCED MICROWAVE ANALOG MULTIPLIER 6 Claims, 1 Drawing Fig.

[52] US. Cl 321/69, 235/179, 235/194, 307/229, 333/11 [51] Int. Cl. [102m 5/20 [50] Field ofSearch 307/321,

[56] References Cited UNITED STATES PATENTS 3,300,630 1/1967 Hartenstein 235/194 3,300,631 1/1967 Vallese 328/ 1 60X 3,440,441 4/1969 Ley 307/229 Primary Examiner-Gerald Goldberg Attorneys-R. S. Sciascia and J. A. Cooke ABSTRACT: A completely shielded and balanced diode bridge, having biased diodes to insure dynamic balance and square-law operation, is fed by sum and difference signals from a hybrid ring drive which produces an output signal proportional to the product of the instantaneous amplitudes of the original microwave input signals applied to the hybrid ring drive.

PATENTEUJUN" 1 I971 IIIIIIII'IIIIIIIIIIIIII.

INVENTOR John H. MaHoy ATT RNEY SHIELDED BALANCED MICROWAVE ANALOG MULTIPLIER CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuationinpart of application Ser. No. 671,495, filed Sept. 28, 1967, now abandoned.

BACKGROUND OF THE INVENTION This invention relates generally to microwave signalprocessing apparatus and more particularly to a shielded, balanced microwave analog multiplier.

In signal correlation systems it is generally necessary to multiply two or more input signals to form an analog signal representative of the product of the instantaneous amplitudes of the respective signals. When the input signals are in the microwavefrequency range, special problems are posed and conventional audio frequency circuits are not operative.

Prior art attempts to provide signal multiplication at microwave frequencies include systems for heterodyning the signals down to a low frequency range and using a conventional ring modulator as a multiplier bridge as described by Page, Brodzinsky and Zirm in the Proceedings of the I.R.E. for Jan. 1953 at page 128. Heterodyning suffers from the disadvantage of not operating at the original microwave frequencies thus requiring an excessive number of components, several of them active.

A passive multiplier, operating at the original microwave frequencies, is described by Wilcox in the Proceedings of the I.R.E. for Oct. 1954 at page 1513. While a passive multiplier device of this type provides a direct multiplication of the input amplitudes, the device is inherently unbalanced because the coaxial inputs short out one of the four diodes in the ring modulator causing a DC bias in the output which may be undesirable. In addition, the device is not RF shielded beyond the coaxial inputs thereby making possible pickup of undesired signals and causing deterioration of the signal-to-noise ratio. Also, this type of device does not provide for biasing the diodes to provide a balance adjustment and to insure operation in the desired square-law region of the diodes which is required if the output is to be representative of the product of the instantaneous amplitudes of the applied microwave signals. Still furthermore, this type of device is not adaptable to planar design, that is, it has crossovers thereby precluding certain construction techniques such as stripline, integrated RF circuitry or the like.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide an improved passive analog multiplier particularly suitable for operation in the microwave frequency range.

Another object of the present invention is to provide a balanced microwave analog signal multiplier.

A still further object of the instant invention is to provide an analog multiplier operable in the microwave frequency range having an improved signal-to-noise ratio.

Yet another object of this invention is to provide a microwave signal multiplier with total electromagnetic shieldmg.

Still another object of the present invention is to provide an analog signal multiplier adaptable to miniature microwave planar construction.

Briefly, in accordance with one embodiment of the invention, these and other objects are attained by providing in a shielded, balanced analog signal multiplier operable at the microwave frequency range the combination of a four arm bridge having unidirectional elements therein, a hybrid ring drive which produces the sum and difference signals of two input microwave frequency signals and which sum and difference signals are applied to two opposite corners of the bridge, respectively, and two load devices connectable across the other corners of the bridge across which the product of the instantaneous amplitudes of the original input signals is available.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will be readily appreciated as the same becomes better understood by reference to the following description when considered in connection with the accompanying drawing wherein the solitary FIG. is a schematic view of the shielded microwave analog multiplier according to the present invention.

DESCRIPTION OF THE REFERRED EMBODIMENT The figure shows and analog signal multiplier operable at microwave frequencies as including a completely shielded four arm diode bridge I having unidirectional conducting elements such as diodes 2, 3,.4 and 5 and a conventional hybrid ring drive 6 capable of receiving two input signals of microwave frequency having instantaneous amplitudes E, and E respectively, which are to be multiplied. The hybrid ring drive processes the input signals in the manner known in the art to provide sum and difference signals, k(E,+E and k(E, E which are applied to opposite junction points 7 and 8, respectively, of the diode bridge 1. The hybrid ring drive decouples ground from the diodes thereby insuring that the shielding will not short out one of the diodes and, thereby, convert the four-diode balanced system to a less desirable three-diode unbalanced system.

Load devices such as resistors 9 and 10 are connectable between the remaining junction points 11 and 12 of the diode bridge. The junction of resistors 9 and 10 is grounded. Reactive impedance elements such as chokes l3 and 14 are connected to junction points 11 and 12, respectively, to block microwave energy and pass low frequency signals and to provide the analog output, kE,E between terminals 15 and 16.

An adjustable DC bias is provided for each diode in the bridge by DC bias sources external to the shielded system. A plurality of reactive impedance elements, such as chokes 17, 18, 19, 20, 21, 22, 23 and 24 block microwave energy and isolate the DC bias sources from the bridge. DC voltage supplies 25, 26, 27 and 28 and variable resistance devices, such as potentiometers 29, 30, 31 and 32 located externally to the shielded system, are connected to each diode, respectively, and, as hereinbefore mentioned, provide a variable DC bias for each diode.

In operation, the DC bias voltages are adjusted so that each diode is forward biased in the center of its square-law (i=kv operating region. As hereinbefore explained, each diode may be adjusted to operate in its square-law range which is advantageous if the output signal between terminals 15 and 16 is to represent the analog product of the instantaneous amplitudes of the applied input signals. Furthermore, as hereinbefore explained, the individual DC bias for each diode insures that a balanced four-diode system may be obtained which contains no DC bias output component, the DC bias output component being an undesirable trait in heretofore employed nonbalanced systems. Thus, when the diodes are properly biased, an output of the form kE,E may be obtained across terminals 15 and 16, responsive to the input of the hybrid ring drive, without an undesirable DC component in the output.

It is to be particularly noted that the entire device, except for the DC bias sources and potentiometers, is totally shielded from external electromagnetic radiation and stray RF signals. The ability of the instant invention to provide a completely shielded system is a distinct advantage over the prior art which, heretofore, has been unable to completely shield the multipliers, at least without shorting out one of the diodes in the bridge. Thus, the prior art multipliers have been forced to sacrifice wither shielding, which is important at microwave frequencies, or a balanced four-diode system, which is advantageous in operation, or both.

The microwave multiplier described will provide simple and reliable analog multiplication of microwave signals. By providing true balance and complete shielding a significant increase in signal-to-noise ratio over prior art devices may be obtained.

It is readily apparent that any transmission line mode may be utilized to fabricate the multiplier. Thus, coaxial cable, stripline, waveguide and miniature microwave planar fabrication, for example, may be utilized. Furthermore, and desired shielding may be used.

Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. Thus, if one of the input signals is variably delayed with respect to the other and the multiplier output is fed into an integrator, a correlation signal is produced. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What I claim as new and desire to be secured by Letters Patent of the United States is:

1. A shielded, balanced microwave analog multiplier comprising in combination a bridge including four unilaterally conducting devices con nected in series and polarized in the same direction, means for connecting a load between two nonadjacent junctions of said bridge and for connecting an intermediate portion of said load to a point of reference potential, means for providing microwave signals to the remaining two nonadjacent junctions of said bridge whereby a signal proportional to the product of the instantaneous amplitudes of said microwave signals is provided across said load means, and means for shielding said multiplier from external signals. 2. A shielded, balanced microwave analog multiplier according to claim 1 wherein said unilaterally conducting devices comprise diodes. 3. A shielded, balanced microwave analog multiplier according to claim 2, further comprising means for applying a substantially DC bias to forwardly bias said diodes. 4. A shielded, balanced microwave analog multiplier according to claim 3, wherein said diodes are forwardly biased in their square-law regions. 5. A shielded, balanced microwave analog multiplier according to claim 1 wherein said provided microwave signals are proportional to the sum and difference of microwave signals and are applied to the remaining nonadjacent junctions of said bridge, respectively. 6. A shielded, balanced microwave analog multiplier according to claim 5, wherein said means for providing the sum and difference microwave signals comprises a hybrid ring drive. 

1. A shielded, balanced microwave analog multiplier comprising in combination a bridge including four unilaterally conducting devices connected in series and polarized in the same direction, means for connecting a load between two nonadjacent junctions of said bridge and for connecting an intermediate portion of said load to a point of reference potential, means for providing microwave signals to the remaining two nonadjacent junctions of said bridge whereby a signal proportional to the product of the instantaneous amplitudes of said microwave signals is provided across said load means, and means for shielding said multiplier from external signals.
 2. A shielded, balanced microwave analog multiplier according to claim 1 wherein said unilaterally conducting devices comprise diodes.
 3. A shielded, balanced microwave analog multiplier according to claim 2, further comprising means for applying a substantially DC bias to forwardly bias said diodes.
 4. A shielded, balanced microwave analog multiplier according to claim 3, wherein said diodes are forwardly biased in their square-law regions.
 5. A shielded, balanced microwave analog multiplier according to claim 1 wherein said provided microwave signals are proportional to the sum and difference of microwave signals and are applied to the remaining nonadjacent junctions of said bridge, respectively.
 6. A shielded, balanced microwave analog multiplier according to claim 5, wherein said means for providing the sum and difference microwave signals comprises a hybrid ring drive. 